Method of expanding tubing by freezing liquid therein



Jan. 4, 1949. D. E. MORGAN METHOD OF EXPANDING TUBING BY FREEZING LIQUIDTHEREIN 2 Sheets-Sheet 1 Filed July 18, 1945 INVENTOR 'flaqzdfl/i/alyaiz ATTORNEYS Jan. 4, 1949. MORGAN 2,458,189

METHOD OF EXPANDING TUBING BY FREEZING LIQUID THEREIN Filed July 18,1945 2 Sheets-Sheet 2 wi i Q Q;

so" 7 5 L J p:

I;\ C INVENTOR MAETMVM v ATTORNEYS flava'dlzdfozya Patented Jan. 4, 1949METHOD OF EXPANDING TUBING BY FREEZING LIQUID THEBEIN David E. Morgan,Philadelphia, Pa., assignor to Warren Webster & Company, Camden, N. J.,a corporation of New Jersey Application July 18', 1945, Serial No.605,898

4 Claims.

This invention relates to methods for utilizing the expansion forcesoccurring upon the solidifying of liquid or molten materials uponlowering the temperature thereof, for the purpose of expanding oraltering the shape of tubular containers and the like.

The various features of the invention are adapted to a number ofdifferent purposes. For example, in the manufacture of finned tubingsuch as is used for radiation purposes or otherwise, it is a difficultproblem to firmly and permanently secure the fins in place on the tubingand in a manner to insure such uniformly good contact between the finsand tubing as will make possible the efficient transfer of heat. Themethods heretofore available for this purpose have, so far as is known,involved serious difficulties. For example, one method has been to applythe fins one after another with a forced fit, on to the tubing. This hasthe difilculty of involving successive operations individual to eachfin, and also as a succession of the fins are forced along the free endof the tube, the tubing becomes smaller and smaller so that the productis not uniform from end to end.

Other methods have involved placing the fins on the tubing and thendrawing or projecting an expanding device through the tubing so that thetube walls are expanded into contact with the fins. These operations arerelatively expensive and involve various mechanical difficulties, andare also generally impossible of application to tubing after it has beenbent or substantially curved.

In accordance with the present invention, the succession of the fins maybe first placed along the tubing in the desired spaced relation and thenthe tubing is filled with water or other liquid or molten material whichwill expand on solidifying. Then under controlled conditions, theassembly is subjected to temperatures low enough to cause freezing orsolidifying of the contents, with the result that the tubing is expandedinto firm contact with the inner edges of all of the fins.

While of course it has long been recognized that pipes or containers,upon the freezing of liquid therein, will become expanded, insofar as isknown, no methods have been available for so controlling such expansionthat the results could be put to the practical uses accomplished by thepresent invention.

As will be hereinafter further explained, the invention, in addition toits application to the securing of fins to tubing, may also be simul-- 2taneously or separately utilized for reshaping the tubing, for example,to form a series of annular corrugations in the walls thereof. I havediscovered further that the metal tubing when subjected to controlledexpansion according to the invention may also be hardened thereby, tovarying degrees as desired. Also the invention is well adapted to thecontrolled expansion of tubing in order to permanently secure the tubingwithin surrounding parts other than fins, such for example, ascontinuous sheaths or surrounding pieces of tubing which are formedeither of the same or other metals or materials, within which the innertube is primarily expanded.

Various further and more specific objects, features and advantages ofthe invention will appear from the detailed description given belowtaken in connection with the accompanying drawings which form a part ofthis specification and illustrate by way of example. preferred forms ofthe invention. The invention consists in such novel combinations ofparts, methods and method steps as may be shown and described inconnection with the apparatus herein disclosed.

In the drawings, v

Fig. 1 is an elevational view, partially broken away and partially insection, illustrating one embodiment of the invention;

Figs. 2 and 3 are elevational views respectively, showing two otherembodiments of the invention;

Fig. 4 diagrammatically indicates one method according to which thefreezing and subsequent thawing steps may be carried out in accordancewith the invention;

Fig. 5 is an enlarged detailed view showing portions of a tube structurewith surrounding fins secured thereon in accordance with the invention;

Fig. 6 illustrates a section of bent tubing with fins placed thereon inaccordance with the invention;

Fig. 7 illustrates one form of radiator structure which may be madeaccording to the invention;

Fig. 8 diagrammatically indicates the manner in which tubing may beexpanded to form annular corrugations thereon in accordance with theinvention;

Fig. 9 illustrates a section of tubing which has been expanded to fitwithin an outer length of tubing according to the invention; and

Figs. 10-12, inclusive, are sectional views of alternative arrangementsof apparatus for carrying out the invention.

The proper control of the expansion effects upon the freezing of theliquid within the container, involves a number of factors which have tobe carefully taken into consideration in order to obtain practical,accurate and uniform results. First it should be noted that the volumeof the liquid to be frozen should be securely confined, since the liquidupon freezing, expands into regions of least resistance. Thus, in thecase of normally open ended tubes, it is necessary while performing themethod, to provide some means to firmly plug the ends of the tubes aftersame have been filled with the medium to be frozen. This in some cases,may be accomplished by threading the ends of the tube and applyingordinary pipe caps or the like. However, if the tube is of suchdimensions as would require use of such a cap or the like embodying aconsiderable mass of metal, it has been found that the freezingwilloccur first within the middle portions of the tubes and thatexcessive bulging will occur at the ends when freezing finally takesplace there with consequent unsatisfactory and non-uniform expansioneffects.

To overcome this diiiiculty, one form of end closure arrangement whichhas been found to give satisfactory results is illustrated in Fig. 1.Here the tubing which is to be expanded is indicated at l l surroundedby a plurality of radiating fins I2 which have been placed on the tubeat the desired positions at which it is intended to have the samesecured by reason of the expansion of the tube l I.

The tube II, for example, may be formed of copper and the fins l2 may beformed, for example, of copper or aluminum and may be either of a,rectangular, square or circular shape, and formed with a centralaperture in which the tube, II is received. If desired, the inner edgesof the fins around the aperture may be flanged as at 13, these flangesbeing preferably of suitable width tobprovide spacing means for the finsalong the tu e.

As shown in Fig. 1, the end edges of the tube may be first flaredoutwardly somewhat as indicated at M, and after the tube has been filledwith the medium which is to be frozen, such as water, a tapered plug asat l5 may be inserted and forced into the flared tube end. This plug maybe formed, for example, of synthetic resin material such as a phenolformaldehyde condensation product. The tube end may then be surroundedby a hollow split, externally tapered, synthetic resin ring formed forexample at two parts,

l6 and Mia, separable along a plane I! which.

preferably passes through the axis of the tube.

As indicated, the upper surfaces l8 of this twopart split ring mayengage at their inner edges agz inst the flared tube portion l4, and thesplit ring may-be surrounded by an internally tapered rigid steel ringas at I9 recessed at its lower edge as at 20, to receive inwardlydirected portions 2| and 22 of a rigid steel clamping member 23. The

upper portion of the clamping member 23 as shown, may extenddiametrically across the assembly and may be threaded to receive a clamping screw 24, the lower end of which bears against the plug I 5. Upontightening the screw 24, it

will be apparent that the plug I5 will be forced firmly into position toclose the end of the tube,

since the clamping member grips the steel ring l9, which in turn bearsinternally against the split insulation ring Iii-Ilia and the latterpresses up against the flared tube end It, With this arrangement, itwill be apparent that through the use of a plug and split ring ofsynthetic material which is a good heat insulator, the WW 4 walls arekept out of contact with any metal parts of good heat conductivity or ofsubstantial mass. If the necessarily relatively massive parts of theclamping or plugging means are not thus made of insulation material orinsulated from the tube walls, then upon subjecting the assembly tofreezing temperatures, the expansion effects will as above stated, notbe uniform. The reasons for this are believed to be as follows. Heatwill be readily dissipated through the exposed thin walls of the middleportions of the tube, with consequent rapid freezing action within theseportions. At the same time, before the end portions of the assembly arecooled t freezing temperature, considerable heat would have to beconducted from the metal masses of the clamping parts or plug. into andthrough the walls of the end of the tube and along the tube into themore exposed cooler Thus, freezing is middle portions of the tube.delayed at the e." 6. portions until after such portions have beensubjected to high internal pressures for some time, due to the expansionof the freezing medium at the middle portions. Hence, by the timefreezing occurs in the end portions, they will have become excessivelybulged. For this and possibly other reasons, it has been found highlydesirable for satisfactory results to use some form of end closure meanswhich will avoid any substantial masses of metal in contact with the endof the tube.

With the arrangement shown in Fig. 1, it has been found that thefreezing action occurs substantially concurrently throughout the lengthof the tube including the end portions, and therefore, the expansioneffects are substantially the same adjacent the end portions as at themiddle portions of the tube.

- It will be understood that the opposite end of the tube ll may also beclosed by an arrangement similar to that shown in Fig. 1.

In order to control the expansion within carefully predetermined limits,it is necessary to use a predetermined volume of the medium to befrozen, such volume being determined upon takinginto account thepercentage by which the particular freezing medium used will expand uponlowering the temperature and solidifying it,

For example, if the medium used is water, its volume will expand byapproximately 8.55% upon passing from the fluid to the solid state, andthe linear coefiicient of expansion of ice is 0.0000507 per C., whichfactor may also in some cases, have to be taken into consideration,especially if low quick freezing temperatures are used. It will beapparent that if for example, the internal diameter of the tube isrelatively large and if the walls are thin, they may not be able towithstand the 8.55% expansion, if the tubing is entirely filled withwater. Even if the walls are able to withstand such expansion, thepercentage of expansion may be greater than desired.

Thus, in order to control the amount of expansion within the desiredlimits, either some fluid medium has to be selected which will have thedesired degree of expansion, taking into consideration the dimensions ofthe container, or preferably one may introduce a solid object into thecontainer so that if for example, water is used as a freezing medium,its volume will be limited to a predetermined amount just suflicient toaccomor other fluid within the tube to the amount necessary to securethe desired expansion effect.

Assuming for practical purposes that such rod is of the same length asthe tube, the rod diameter may be determined by the following formula:

2 2 1 C where D equals the diameter of the rod, D1 is the initialinternal tube diameter, D: is the final internal diameter, and C (incase water is used) equals 0.0855. For example, if the initial internaldiameter of the tube is 4 inches and it is desired to expand suchdiameter to 4.05 inches, then it may be calculated according to theabove formula, that the diameter of the rod should be 0.94 inch. It willbe understood that if liquids other than water are used, the value of Cin the above formula would be changed, depending upon the percentage bywhich the medium expands upon passing from the fluid to a solid state.

It has been found when using a rod as at 25 in Fig. 1, that it isimportant to retain such rod throughout its length substantially in itscentral position as shown. bend into proximity of the tube walls, therate of freezing at these areas as compared with other regions withinthe tube will be varied, and the resulting expansion effects will benon-uniform longitudinally of the tube and around the tube. A convenientmethod of holding the rod in the desired axial position is to use one ormore guide discs thereon as at 26, formed for example, of thermoplasticor other heat insulating material and having central apertures forreceiving the rod. If special shapes are desired with nonsymmetrical orirregular expansion around the walls of the tube, a rod as indicated indotted lines at 25 may be inserted and held in a desired non-axial orcurved position by using guide discs with off-center apertures.

During the freezing action, the tubes will of course expand in length aswell as in diameter, but if the expansion is controlled as abovedescribed, the expansion in length is ordinarily negligible for tubingsuch as used for radiation purposes and the like.

It has been found that with copper tubes, at least of dimensionscustomarily used for radiation purposes, it is essential that the tubingfirst be annealed before being expanded in accordance with thisinvention, since if tubing of hard copper is used, the expansion effectwill almost invariably cause rupture. It has been further found thatupon expanding the tubing by the method of this invention, the initialannealed tubing becomes to a considerable degree hard ened as a resultof the expanding action. In some cases this hardening action isdesirable in that it renders the tube more rigid so that in case finsare to be secured in place by the method, they will be less apt tobecome loosened in view of the finally hardened and rigid character ofthe tubing. In cases where it is desired to avoid a hardened finalproduct, it of course may be annealed again after expanding.

Fig. 2 illustrates another arrangement for closing the ends of the tube.In this case, cap members as at of suitable thermoplastic or other heatinsulating material, may be provided for each end of the tube and thesemay be clamped and held in place by a through bolt 3|, extending axiallythroughout the tube. Such bolt may preferably be of a diametercalculated in accordance with the same principles as above explained Ifany portions of the rodin connection with the rod 25 of Fig. 1.Accordingiy, the same bolt or rod may serve a dual purpose of securingthe caps in place and of limiting the volume of the freezing medium to adesired predetermined amount.

From the standpoint of facilitating rapid production however, thearrangement of Fig. 1 is generally preferable over that of Fig. 2.

Fig. 3 illustrates another alternative arrangement for sealing the endsof the tubes, this ar-.

rangement as shown being adapted for providing closure means for anassembly of a plurality of the tubes as at II, II. In this case, eachend of each tube may be provided with an insulation closure cap as at35. These caps may be held in place by bars or plates of plasticinsulation material as at 36, the latter'in turn being clamped betweenrigid end plates 37, by the action of through bolts as at 38. It will beunderstood that rods such as at 25 of Fig. 1, with accompanying.retaining meanssuch as discs 26, may also be used within the tubes ofFig. 3.

Fig. 4 illustrates somewhat diagrammatically the manner in whichassemblies such as at Figs. 1-3 may, after preparation be supported upona conveyor belt 40 and carried into, through and out of a suitablefreezing bath as at 4|, thence into, through and out of a thawing bathas at 42. The speed of the conveyor belt, the dimensions of the freezingtank and the temperature of the refrigerant therein may of course besuitably adjusted depending upon the time required for the particulartube and closure assemblies being treated, to become cooled to freezingtemperature. Also the dimensions and temperature of the thawing bath maybe varied, depending upon the time re,- quired for the assemblies tobecome warmed to a temperature sufiicient to thaw the freezing mediumwithin the tubes. If desired, the thawing bath may contain or beaccompanied by a heating coil as at 43. Also this bath may incorporateany suitable cleaning fluid for eifectively cleaning the exteriorsurfaces of the tube and fins as the assemblies pass through. After theassemblies have been withdrawn from the thawing bath, theend closuresmay .be removed to permit discharge of the freezing medium.

In most cases, it appears advisable to use a freezing bath of relativelylow temperature so as to cause rapid and more uniform freezingthroughout the volume of liquid within the tubes, a temperature of 20 F.being satisfactory.

If the walls of the tubing are relatively thin and if the fins l2 areprovided with flanges [3 which are relatively thin, as will usually bethe case, then the expansion of the tubing according to this invention,will result in the formation of slight annular corrugations as shown inthe enlarged view of Fig. 5. That is, along circumferential lines of thetubing which are engaged by the surrounding main body portions of thefins, the tubing will be restrained somewhat against expansion ascompared with the surface portions which are surrounded only by therelatively yieldable flanges l3. Accordingly, a slight outward bulgingor corrugation will form beneath each of the flanges l3, and this bulgewill be of a shape such as to tend to firmly lock the fin'and its flangein position on the tube. This offers a substahtial advantage,particularly where the finned tubing is to be used for radiationpurposes and where the temperature of the tube may vary withinconsiderable limits from time to'time, thereby causing contraction andexpansion dimculties 7- which would tend toloosen the fins in theabsence of such locking eflect.

The corrugations also aid in preventing difllculties due to elongationof the finned tubing by reason of thermal expansion when the tubing isused in radiator structures. Thatls, the corrugations tend to impart acertain degree of longitudinal flexibility, and at the same time reducethermal expansion longitudinally. Furthermore, the corrugation of finsformed exceptionally thin flexible material. For example, fins of thinaluminum may be applied to copper tubes with a considerable saving ascompared with what has been obtainable with prior art structures ofequivalent radiation capacity.

With the prior art mechanical methods for applying and securing the finsas-herein above referred to, it is necessary that the tubing remain,substantially straight, at least until after the fins are secured inplace and thereafter it is substantially impossible to bend the assemblyto form loops or turns in the tubing without loosening or effl'ectfacilitates the firm securing medium and equipped with. end closuremeans as displacing the fins. On the other hand, with the presentinvention as indicated in Fig. 6, the tubing may be initially bent toconform to various desired curved shapes, such as a grid shape, Then thefins may be slipped on to the desired positions and thereafter firmlysecured in place by the freezing and expansion method of this invention.If desired, long grids of radiation structure, may be made of the formindicated in Fig. 6 and kept in stock. Then these may be cut intosections of any desired heating capacity as needed, as by cutting thetube along a line such as indicated by the dot-dash line 45.

This embodiment of the invention makes it possible to provide finned Utubes with any desired number of "turns without resorting to sol- :leredor braised connections as has heretofore been the necessary practice forfinned U tubes.

With the tube bent as in Fig. 6, in order to obtain the desiredpredetermined degree of expansion, one may either select a kind offreezing liquid which for the volume present, will give the desiredexpansion, or a rod as at in Fig. 1, may be inserted and left within theassembly permanently, if desired. Also a removable rod of flexibleplastic material might be used.

As shown in Fig. 7, a plurality of the tubes as at Ila to lie,inclusive, may all be treated as a group, according to the invention,for the application of fins as at l2a which extend continuously fromtube to tube. After the tubes have been expanded to firmly secure thesefins thereon in accordance with the principles above described,.the'assembly oftubes may be provided with headers as at 50, 5| into whichthe tubes may be brazed or otherwise sealed. Such an assembly may bemade with any number of tubes to secure a radiator of desired capacity.When smaller radiators are called for, the assembly may be cut, as forexample, along the dash line indicated at 52, thereby cutting throughthe headers as well as the fins.

The embodiment. of Fig. '7 makes possible a desired configurations ontubing which isnot to. Y be. provided with fins. For. example, as shownof Figs. 1-3, may be inserted within an aperture of a die member 56,this member having an ini ternal aperture formed with corrugations orother desired configurations so that when the tube is expanded therein,its wall surfaces will be correspondingly corrugated or'shaped. The diemay of course be formed of parts separable as along a center line 51, toenable removal of the expanded tube.

Sheet metal bellows or similar devices, may be made in accordance withthis embodiment of the invention by first expanding an annealed tubewithin a die as at Fig. 8, then annealing the tube,

and again expanding the same within a die hav-' ing deeper corrugations,and repeating this process until the desired form is completed.

Certain features of the invention may also be utilized for the purposeof expanding tubing or the like into firm contact with various othertypes of surrounding structuresjsuch as flanges, conduit joint parts, orfor the expansion for example of tubes into sealing relationship withheaders as in boilers. For example, as indicated the freezing method maybe appliedto the tube 60 in substantially the same manner as indicatedin connection with Fig. 1. This method has an r important advantage overother methods for encasing a tube within an outer shell in that all ofthe outside wall surfaces of the inner tube will be pressed intosubstantially uniform contact with the internal wall surfaces of theouter tube, despite any variations or irregularities which may exist inthe surfaces, such for example, as irregularities indicated at 62. Inview of this fact, the possibility of occurrence of small air pocketsbetween the tubes will-be eliminated.

While with the invention as above described in connection with Figs. 1to 4, the refrigerant for causing freezing is applied to the exterior ofthe tubes, it' is also possible to apply the refrigerant internallyofthe tubes as for example, with apparatus such as indicated in Fig. 10.Here a tube 10 which is to be expanded and which may have With thisarrangement, it will be apparent that the body of freezing medium as at18 located be-' tween the interior walls of tube 10 and the rigidcontainer 14 may be cooled to freezing temperature internally. Thisarrangement may have advantages as in cases where it is undesirable orinconvenient toapply a freezing bath to the external surfaces of thetube or container which is to be expanded.

In case it is desired to expand different portions along the length of atube,'for example, to

various different degrees. this may be accomfrozen, has containedtherein a rod as at ill, the

diameter of which varies from place to place. For example, if at thelefthand end of the tube 80 as shown in Fig. 11, it is desired to causevery little expansion, the rod is made relatively large,

' as at 8la within this portion of the tube. As

indicated, the rod may be tapered and/or varied in diameter according tosteps, so as to leave more space for liquid in other parts of the tubingwhere greater expansion is desired.

In some cases it may be found desirable to expand a tube or other partto a greater degree than would be accomplished by freezing the amount ofliquid contained within the tube itself.

In this case the tube or other cavity to be ex-.

panded may be connected with an external reservoir of the liquid to befrozen. One simple method for accomplishing this is somewhatdiagrammatically indicated in Fig. 12, wherein a tubular part as at B4is shown clamped within a split die member as at 85, having a cavity asat 86 for liquid in addition to the space within the member 84. Whenthis assembly is suitably sealed and clamped with the parts in theposition shown and with the space within the member 84 as well as thecavity 86 filled with liquid, it will 'be apparent upon freezing suchliquid'that portions of the member 84 will be expanded into the cavity81 to a greater extent than would be possible by merely freezing thecontents of member 84 alone.

While the invention has been described with particular reference to itsapplication to tubing, it will be understood that the principles of theinvention are also applicable to the expansion of containers of othershapes.

It will be further understood that instead of using water as thefreezing medium, various liquid chemicals may be used having the desireddegree of expansion upon solidification. Furthermorefthe expansion maybe accomplished by using chemicals which will react with increasedvolume to cause expansion of the tube. Furthermore, metal alloys may beused which will expand when cooled, such as in the case of certainalloys of antimony. These, for example, may be poured into the tube whenhot and on .cooling,

would expand. Thereafter the alloy may be remelted in order to remove itfrom the expanded tube. One commonly known example of such a metal alloyis so-called type metal which normally consists of about 15% antimony,82% lead and 3% tin.

The method of expanding tubes or other containers by freezing liquidtherein, in accordance with this invention, has substantial advantagesover methods heretofore proposed for the use of hydraulic pressure forthe purpose. Expansion by hydraulic pressure will cause the weakestspots or areas in the tube to expand more than other parts and thusresult in irregularities. Also hydraulic pressure for such purposes hasto be closely controlled or over-expansion will result because of thefact that as the walls expand, they will become progressively weaker andthus more susceptible to over-expansion.

When it is desired to use a plurality of the finned tubes assembled withheaders, it may sometimes be found convenient to used the headers as theend closures or sealing means for the tubes during the freezing step. Insuch cases, plastic bushings may be desirable for connecting the tubesto the headers and to provide insulation therebetween to afford moreuniform expansion throughout the length of the tubes.

While the invention has been described in detail with respect toparticular preferred examples, it will be understood by those skilled inthe art after understanding the invention that various changes andmodifications may be made without departing from the spirit and scopeofthe invention, and it is intended therefore in the appended claims tocover all such changes and modifications.

I claim:

1. Method for securing annular fins in positions surrounding a metaltube, which comprises confining within the tube a predetermined volumeof a liquid medium partially and substantially to the" same extentfilling each cross-sectional portion of the tube, said medium beingcapable of expanding on solidifying, limiting the amount of said liquidmedium by substantially filling the remainder of the space of each saidcross-sectional portion within the tube by inserting a substantial- 1ynon-compressible material which is notsubject to a change in state atthe temperature of solidification of said liquid medium, then subjectingsaid liquid medium to a temperature causing such solidification thereof,the volume of said liquid medium being made sufficient to cause uponsuch solidification permanent expansive deformation of the tube intofirm contact with the surround-v ing fins, and the volume of saidmaterial being sufiicient to so limit the volume of said medium uponsolidifying that no rupture of the tube I occurs.

2. Method for forming corrugations in the walls of metal tubing whichcomprises surrounding the tube with means which will tend to retain thetube relatively rigidly against substantial expansion along portionscorresponding to the valleys of the desired corrugations, as comparedwith portions on the tube corresponding to the ridges of the desiredcorrugations, confining within the tube a predetermined volume of aliquid medium partially and substantially to the same extent fillingeach cross-sectional portion of the tube, said medium being capable ofexpanding on solidifying, limiting the amount of said liquid medium bysubstantially filling the remainder of the space of each saidcrosssectional portion within the tube with a substantiallynon-compressible material which is not subject to a change in state atthe temperature of solidification of said liquid medium, then subjectingsaid liquid medium to a temperature causing such solidification thereof,the volume of said liquid medium being made sufficient as compared withthat of said material to cause upon such solidification the formation ofsaid corrugations, but being so limited by the presence of said materialthat no rupture of the tube occurs.

3. Method for causing tubing to be permanently expanded to apredetermined degree, which comprises introducing an axially extendingsolid and substantially non-compressible rod into a tube to provide aspace of predetermined volume between said rod and the interior tubewalls, substantially filling such space with a liquid medium capable ofexpanding on solidifying, then subjecting the liquid medium to atemperature causing such solidification with consequent expansion of thetube walls, the volume of said liquid medium as compared with that ofsaid rod being made suiilcient to cause upon such solidification saidpredetermined permanent degree of file of this patent:

- expansion, but being so limited by the presence of said rod that norupture oi the tube occurs.

4. Method for causing tubing to be permanently expanded to apredetermined degree, which comprises confining within the tubing apredetermined volume of a liquid medium partially and substan-.

- tially to the same extent filling each cross-sectional portion of thetubing, said medium being capable of expanding on solidifying, limitingth amount of said liquid medium by substantially filling the remainderof the space of said crosssectional portions along and within the tubingby introducing a material which is not subject to a change in state atthe temperature of solidiflcation of said medium, but which will resistany substantial compression upon solidification of said medium, thensubjecting said liquid medium to a temperature causing suchsolidification thereof, the relative volumes of said medium and materialbeing such as to cause upon such solidification the said predeterminedpermanent degree. of expansion of the tubing but without rup-' ture ofsame. 1

DAVID E. MORGAN.

REFERENCES CITED The following references are of record in the l2 UNITEDSTATES PATENTS Number Name Date 618,353 Huber Jan. 24, 1899 5 1,057,081Neiman et al. Mar. 25, 1913 1,095,477 Still May 5, 1914 1,733,455Ferrand Oct. 29, 1929 1,764,561 Gulick June 17, 1930 1,812,509 BensonJune, 30, 1931 1,844,123 Holland Feb. 9, 93 1,952,780 Small Mar. 27,1934 1,957,702 Davis, Jr. et al May 8, 1934 2,004,389 Jones June 11,1935 2,038,304 Middler Apr. 21, 1936 2,039,736 Munters May 5, 19362,072,975 Winsborough et al. Mar. 9, 1937 2,119,960 7 Price June 7, 19382,145,473 Billner Jan. 31, 1939 2,181,107 Przyborowski Nov. 21, 19392,245,069 Clarke June 10, 1941 2,350,541 Stulen et al. June 6, 19442,357,447 Benson Sept. 5, 1944 FOREIGN PATENTS Number Country Date630,129 France Aug. 9, 1927

